Proposal Summary Intestinal aging is characterized by a decline in stem cell regeneration and renewal, inflammation, DNA damage, and loss of mucosal barrier integrity, all of which can dramatically raise cancer risk. Despite the fact that the vast majority of cancers arise in older adults, tremendous gaps remain in our understanding of why cancer risk rises exponentially with age, including the role of the aging host?tumor microenvironment interaction in disease pathogenesis. Because many age-related cancers are suspected to arise after decades of cell-intrinsic alterations, it seems intuitive that only long-lived cells (i.e. stem and progenitor) would be susceptible to such manifestations, and serve as the origin of many age-related cancers. Relevant to this proposal, we have developed parabiosis as a tractable system for aging research, and used this approach to demonstrate that intestinal homeostasis is markedly impaired in young mice exposed to old blood, suggesting that these phenotypes are mediated at least in part, by systemic factors. Based upon these data, we hypothesize that the old systemic milieu provokes inflammatory responses in the gut to drive intrinsic aging of the intestine and increase the probability for later transformation and tumorigenesis. We will test this hypothesis by performing two innovative Aims utilizing heterochronic parabiosis. In Aim 1, we will determine the contribution of the intestinal microenvironment versus the old systemic millieu in age-related intestinal decline. We have shown that intestinal decline can be instigated by exposure to old blood and hypothesize that this effect requires an altered gut microenvironment. This will be tested by performing heterochronic parabiosis in combination with genetic models and oral mesalamine treatment, to determine whether gut inflammation is required for the age-related decline in intestinal function by exposure to an old environment. Further, we propose that TNF?, IFN? and IL-1? (local and/or systemic) are key mediators in driving local inflammation and DNA damage, both of which are risk factors for transformation. To that end, we will determine the contribution of TNF?, IFN? or IL-1? inhibition with mAbs to restore normal local immune function, reduce oxidative stress and DNA damage. In Aim 2, we will utilize novel parabiotic pairs to determine the role of cell intrinsic versus cell extrinsic aging to Lgr5+ intestinal stem cell-derived tumorigenesis. Specifically this aim will determine the role of Lgr5+ stem cell intrinsic aging versus systemic aging on tumorigenesis and disease progression in isochronic (Y-Y, O-O) and heterochronic (Y-O) Lgr5EGFP-IRES- creERT2/Apcfl- mice. Further elucidating and validating the role of systemic factors in old blood to intestinal aging and tumorigenesis, will not only shed greater light onto the underlying biology of intestinal decline and transformation, but should also important insights toward new therapeutic targets, in an effort to prevent malignancy and promote healthy aging and longevity in humans.